Updates the Stan submodule to ff57a3027.

stan-buildbot · stan-buildbot · commit efb62ddbd4d0 · 2025-03-22T15:26:01.000-04:00
diff --git a/StanHeaders/inst/include/upstream b/StanHeaders/inst/include/upstream
@@ -1 +1 @@
-Subproject commit 0c44a6dfc030a20e07e5950817046fc7526126e4
+Subproject commit ff57a3027a24df69ba3bcf358ce74dad1aa4ea61
